Quick answer: Exothermic reactions mean that heat has escaped the system. The answer is A. Heat is released.
Must be Selenium (Se). It is two space away from Kr, which means that it needs two extra electron to be like a noble gas, Kr.
a thing, especially a trend or fact, that indicates the state or level of something.
That would be gold, which originally in Latin was aurum, which has the chemical symbol Au. Hope this helps!
